Articles de revues : « Time domain NMR »

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Litvinov, Victor, et Yongfeng Men. « Time-domain NMR in polyolefin research ». Polymer 256 (septembre 2022) : 125205. http://dx.doi.org/10.1016/j.polymer.2022.125205.

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Todt, Harald, Wolfgang Burk, Gisela Guthausen, Andreas Guthausen, Andreas Kamlowski et Dieter Schmalbein. « Quality control with time-domain NMR ». European Journal of Lipid Science and Technology 103, n^o 12 (décembre 2001) : 835–40. http://dx.doi.org/10.1002/1438-9312(200112)103:12<835 ::aid-ejlt835>3.0.co;2-p.

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Bielecki, A., D. B. Zax, A. M. Thayer, J. M. Millar et A. Pines. « Time Domain Zero Field NMR and NQR ». Zeitschrift für Naturforschung A 41, n^o 1-2 (1 février 1986) : 440–44. http://dx.doi.org/10.1515/zna-1986-1-286.

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Field cycling methods are described for the time domain measurement of nuclear quadrupolar and dipolar spectra in zero applied field. Since these techniques do not involve irradiation in zero field, they offer significant advantages in terms of resolution, sensitivity at low frequency, and the accessible range of spin lattice relaxation times. Sample data are shown which illustrate the high sensitivity and resolution attainable. Comparison is made to other field cycling methods, and an outline of basic instrumental requirements is given.

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Le Botlan, D., F. Casseron et F. Lantier. « Polymorphism of sugars studied by time domain NMR ». Analusis 26, n^o 5 (juin 1998) : 198–204. http://dx.doi.org/10.1051/analusis:1998135.

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Romano, Rocco, Maria Teresa Santini et Pietro Luigi Indovina. « A Time-Domain Algorithm for NMR Spectral Normalization ». Journal of Magnetic Resonance 146, n^o 1 (septembre 2000) : 89–99. http://dx.doi.org/10.1006/jmre.2000.2102.

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Pedroso, João, João Camporez, Luciana Belpiede, Rafaela Pinto, José Cipolla-Neto et Jose Donato. « Evaluation of Hepatic Steatosis in Rodents by Time-Domain Nuclear Magnetic Resonance ». Diagnostics 9, n^o 4 (20 novembre 2019) : 198. http://dx.doi.org/10.3390/diagnostics9040198.

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Devices that analyze body composition of rodents by time-domain nuclear magnetic resonance (TD-NMR) are becoming popular in research centers that study metabolism. Theoretically, TD-NMR devices can also evaluate lipid content in isolated tissues. However, the accuracy of TD-NMR to determine hepatic steatosis in the liver of small laboratory animals has not been evaluated in detail. We observed that TD-NMR was able to detect increased lipid content in the liver of rats consuming high-fat diet (HFD) for 12 weeks and in genetically obese (Lepob/ob and Leprdb/db) mice. The lipid content determined by TD-NMR showed a positive correlation with triglyceride content measured by colorimetric assays. In contrast, TD-NMR did not detect hepatic steatosis in C57BL/6 mice consuming HFD for 4 or 12 weeks, despite their obesity and increased liver triglyceride content. These findings indicate that tissue mass and the severity of hepatic steatosis affect the sensitivity of TD-NMR to detect liver lipid content.

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Rodrigues, Elton J. R., Pedro J. O. Sebastião et Maria I. B. Tavares. « 1H time domain NMR real time monitoring of polyacrylamide hydrogels synthesis ». Polymer Testing 60 (juillet 2017) : 396–404. http://dx.doi.org/10.1016/j.polymertesting.2017.04.028.

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Rodrigues, Elton Jorge da Rocha, Maxwell de Paula Cavalcante et Maria Inês Bruno Tavares. « Time domain NMR evaluation of poly(vinyl alcohol) xerogels ». Polímeros 26, n^o 3 (8 août 2016) : 221–27. http://dx.doi.org/10.1590/0104-1428.2093.

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Witek, M., H. Peemoeller, J. Szymońska et B. Blicharska. « Investigation of Starch Hydration by 2D Time Domain NMR ». Acta Physica Polonica A 109, n^o 3 (mars 2006) : 359–64. http://dx.doi.org/10.12693/aphyspola.109.359.

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Coggins, Brian E., et Pei Zhou. « Sampling of the NMR time domain along concentric rings ». Journal of Magnetic Resonance 184, n^o 2 (février 2007) : 207–21. http://dx.doi.org/10.1016/j.jmr.2006.10.002.

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Kazimierczuk, Krzysztof, Anna Zawadzka et Wiktor Koźmiński. « Optimization of random time domain sampling in multidimensional NMR ». Journal of Magnetic Resonance 192, n^o 1 (mai 2008) : 123–30. http://dx.doi.org/10.1016/j.jmr.2008.02.003.

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Ghosh, Arindam, Yibing Wu, Yunfen He et Thomas Szyperski. « Theory of mirrored time domain sampling for NMR spectroscopy ». Journal of Magnetic Resonance 213, n^o 1 (décembre 2011) : 46–57. http://dx.doi.org/10.1016/j.jmr.2011.08.037.

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Rössler, Ernst. « Two-dimensional exchange NMR analysed in the time domain ». Chemical Physics Letters 128, n^o 3 (juillet 1986) : 330–34. http://dx.doi.org/10.1016/0009-2614(86)80350-5.

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Rosen, M. E. « Selective Detection in NMR by Time-Domain Digital Filtering ». Journal of Magnetic Resonance, Series A 107, n^o 1 (mars 1994) : 119–25. http://dx.doi.org/10.1006/jmra.1994.1057.

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TODT, H., G. GUTHAUSEN, W. BURK, D. SCHMALBEIN et A. KAMLOWSKI. « Water/moisture and fat analysis by time-domain NMR ». Food Chemistry 96, n^o 3 (juin 2006) : 436–40. http://dx.doi.org/10.1016/j.foodchem.2005.04.032.

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Nascimento, Paloma Andrade Martins, Paulo Lopes Barsanelli, Ana Paula Rebellato, Juliana Azevedo Lima Pallone, Luiz Alberto Colnago et Fabíola Manhas Verbi Pereira. « Time-Domain Nuclear Magnetic Resonance (TD-NMR) and Chemometrics for Determination of Fat Content in Commercial Products of Milk Powder ». Journal of AOAC INTERNATIONAL 100, n^o 2 (1 mars 2017) : 330–34. http://dx.doi.org/10.5740/jaoacint.16-0408.

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Abstract This study shows the use of time-domain (TD)-NMR transverse relaxation (T2) data and chemometrics in the nondestructive determination of fat content for powdered food samples such as commercial dried milk products. Most proposed NMR spectroscopy methods for measuring fat content correlate free induction decay or echo intensities with the sample's mass. The need for the sample's mass limits the analytical frequency of NMR determination, because weighing the samples is an additional step in this procedure. Therefore, the method proposed here is based on a multivariate model of T2 decay, measured with Carr-Purcell-Meiboom-Gill pulse sequence and reference values of fat content. The TD-NMR spectroscopy method shows high correlation (r = 0.95) with the lipid content, determined by the standard extraction method of Bligh and Dyer. For comparison, fat content determination was also performed using a multivariate model with near-IR (NIR) spectroscopy, which is also a nondestructive method. The advantages of the proposed TD-NMR methodare that it (1) minimizes toxic residue generation, (2) performs measurements with high analytical frequency (a few seconds per analysis), and (3) does not require sample preparation (such as pelleting, needed for NIR spectroscopy analyses) or weighing the samples.

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Nikolskaya, Ekaterina, Petri Janhunen, Mikko Haapalainen et Yrjö Hiltunen. « Solids Content of Black Liquor Measured by Online Time-Domain NMR ». Applied Sciences 9, n^o 10 (27 mai 2019) : 2169. http://dx.doi.org/10.3390/app9102169.

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Black liquor, a valuable by-product of the pulp production process, is used for the recovery of chemicals and serves as an energy source for the pulp mill. Before entering the recovery unit, black liquor runs through several stages of evaporation, wherein the solids content (SC) can be used to control the evaporation effectiveness. In the current study, the time-domain nuclear magnetic resonance (TD-NMR) technique was applied to determine the SC of black liquor. The TD-NMR system was modified for flowing samples, so that the black liquor could be pumped through the system, followed by the measurement of the spin-spin relaxation rate, R2. A temperature correction was also applied to reduce deviations in the R2 caused by the sample temperature. The SC was calculated based on a linear model between the R2 and the SC values determined gravimetrically, where good agreement was shown. The online TD-NMR system was tested at a pulp mill for the SC estimation of weak black liquor over seven days without any fouling, which demonstrated the feasibility of the method in a harsh industrial environment. Therefore, the potential of the TD-NMR technology as a technique for controlling the black liquor evaporation process was demonstrated.

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Besghini, Denise, Michele Mauri et Roberto Simonutti. « Time Domain NMR in Polymer Science : From the Laboratory to the Industry ». Applied Sciences 9, n^o 9 (30 avril 2019) : 1801. http://dx.doi.org/10.3390/app9091801.

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Highly controlled polymers and nanostructures are increasingly translated from the lab to the industry. Together with the industrialization of complex systems from renewable sources, a paradigm change in the processing of plastics and rubbers is underway, requiring a new generation of analytical tools. Here, we present the recent developments in time domain NMR (TD-NMR), starting with an introduction of the methods. Several examples illustrate the new take on traditional issues like the measurement of crosslink density in vulcanized rubber or the monitoring of crystallization kinetics, as well as the unique information that can be extracted from multiphase, nanophase and composite materials. Generally, TD-NMR is capable of determining structural parameters that are in agreement with other techniques and with the final macroscopic properties of industrial interest, as well as reveal details on the local homogeneity that are difficult to obtain otherwise. Considering its moderate technical and space requirements of performing, TD-NMR is a good candidate for assisting product and process development in several applications throughout the rubber, plastics, composites and adhesives industry.

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Xin, Gao, Zhou Fan, Fu Zongying et Zhou Yongdong. « A study of pine resin in softwood by 1D and 2D time-domain NMR ». Holzforschung 74, n^o 9 (25 septembre 2020) : 839–52. http://dx.doi.org/10.1515/hf-2019-0001.

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AbstractTime-domain nuclear magnetic resonance (TD-NMR) is widely used in the investigation of wood-water relationship. However, some ambiguities between the NMR signals and the components in wood remain unresolved, particularly the effect of pine resin on NMR signals. To clarify these ambiguities and increase the use of TD-NMR in wood research, different sample treatment methods were studied, including air-drying, low-temperature vacuum-drying, diethyl ether extraction and moisture isothermal adsorption. The corresponding one-dimensional (1D) T1, T2 and two-dimensional (2D) T1-T2 correlation relaxation time distributions of radiata pine and Douglas fir samples were investigated. The NMR signals accounted for “longer relaxation-time components” below the fiber saturation point (FSP), but overlaped in parts of the 1D relaxation time distributions making it difficult to distinguish between pine resin and moisture. The 2D T1-T2 correlation relaxation time distributions produced a better distinction between pine resin and bound water. This distinction established a quantitative relationship between pine resin, moisture and 2D NMR signal amplitudes.

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Pakoulev, Andrei V., Mark A. Rickard, Kent A. Meyer, Kathryn Kornau, Nathan A. Mathew, David E. Thompson et John C. Wright. « Mixed Frequency/Time Domain Optical Analogues of Heteronuclear Multidimensional NMR ». Journal of Physical Chemistry A 110, n^o 10 (mars 2006) : 3352–55. http://dx.doi.org/10.1021/jp057339y.

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Schwartz, Leslie J. « A step-by-step picture of pulsed (time domain) NMR ». Journal of Chemical Education 65, n^o 9 (septembre 1988) : 752. http://dx.doi.org/10.1021/ed065p752.

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Schwartz, Leslie. « A step by step picture of pulsed (time domain) NMR ». Journal of Chemical Education 65, n^o 11 (novembre 1988) : 959. http://dx.doi.org/10.1021/ed065p959.

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Shao, Xiaolong, Wen Xu, Shuihong Xu, Changrui Xing, Chao Ding et Qin Liu. « Time-Domain NMR Applied to Sitophilus zeamais Motschulsky/Wheat Detection ». Journal of Agricultural and Food Chemistry 67, n^o 45 (16 octobre 2019) : 12565–75. http://dx.doi.org/10.1021/acs.jafc.9b04007.

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Digennaro, Frank S., et David Cowburn. « Parametric estimation of time-domain NMR signals using simulated annealing ». Journal of Magnetic Resonance (1969) 96, n^o 3 (février 1992) : 582–88. http://dx.doi.org/10.1016/0022-2364(92)90343-6.

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Lemmerling, Philippe, Leentje Vanhamme, Rocco Romano et Sabine Van Huffel. « A Subspace Time-Domain Algorithm for Automated NMR Spectral Normalization ». Journal of Magnetic Resonance 157, n^o 2 (août 2002) : 190–99. http://dx.doi.org/10.1006/jmre.2002.2598.

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Rutledge, D. N., A. S. Barros et F. Gaudard. « ANOVA and factor analysis applied to time domain NMR signals ». Magnetic Resonance in Chemistry 35, n^o 13 (décembre 1997) : S13—S21. http://dx.doi.org/10.1002/(sici)1097-458x(199712)35:133.0.co;2-p.

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Li, Jingyu, et Erni Ma. « Characterization of Water in Wood by Time-Domain Nuclear Magnetic Resonance Spectroscopy (TD-NMR) : A Review ». Forests 12, n^o 7 (7 juillet 2021) : 886. http://dx.doi.org/10.3390/f12070886.

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This review summarizes the development of the experimental technique and analytical method for using TD-NMR to study wood-water interactions in recent years. We briefly introduce the general concept of TD-NMR and magnetic resonance imaging (MRI), and demonstrate their applications for characterizing the following aspects of wood-water interactions: water state, fiber saturation state, water distribution at the cellular scale, and water migration in wood. The aim of this review is to provide an overview of the utilizations and future research opportunities of TD-NMR in wood-water relations. It should be noted that this review does not cover the NMR methods that provide chemical resolution of wood macromolecules, such as solid-state NMR.

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Segar, Jeffrey L., Kirthikaa Balapattabi, John J. Reho, Connie C. Grobe, Colin M. L. Burnett et Justin L. Grobe. « Quantification of body fluid compartmentalization by combined time-domain nuclear magnetic resonance and bioimpedance spectroscopy ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 320, n^o 1 (1 janvier 2021) : R44—R54. http://dx.doi.org/10.1152/ajpregu.00227.2020.

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The measurement of fluid compartmentalization, or the distribution of fluid volume between extracellular (ECF) and intracellular (ICF) spaces, historically requires complicated, burdensome, and often terminal methodologies that do not permit repeated or longitudinal experiments. New technologies including time-domain nuclear magnetic resonance (TD-NMR)-based methods allow for highly accurate measurements of total body water (TBW) within minutes in a noninvasive manner, but do not permit dissection of ECF versus ICF reservoirs. In contrast, methods such as bioimpedance spectroscopy (BIS) allow dissection of ECF versus ICF reservoirs but are hampered by dependence on many nuanced details in data collection that undermine confidence in experimental results. Here, we present a novel combinatorial use of these two technologies (NMR/BIS) to improve the accuracy of BIS-based assessments of ECF and ICF, while maintaining the advantages of these minimally invasive methods. Briefly, mice undergo TD-NMR and BIS-based measures, and then fat masses as derived by TD-NMR are used to correct BIS outputs. Mice of the C57BL/6J background were studied using NMR/BIS methods to assess the effects of acute furosemide injection and diet-induced obesity on fluid compartmentalization, and to examine the influence of sex, body mass and composition, and diet on TBW, ECF, and ICF. We discovered that in mice, sex and body size/composition have substantial and interactive effects on fluid compartmentalization. We propose that the combinatorial use of NMR/BIS methods will enable a revisioning of the types of longitudinal, kinetic studies that can be performed to understand the impact of various interventions on body fluid homeostasis.

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Igreja Nascimento Mitre, Cirlei, Bruna Ferreira Gomes, Elaine Paris, Carlos Manuel Silva Lobo, Christina Roth et Luiz Alberto Colnago. « Use of Time Domain Nuclear Magnetic Resonance Relaxometry to Monitor the Effect of Magnetic Field on the Copper Corrosion Rate in Real Time ». Magnetochemistry 8, n^o 4 (6 avril 2022) : 40. http://dx.doi.org/10.3390/magnetochemistry8040040.

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The corrosion of metals is a major problem of modern societies, demanding new technologies and studies to understand and minimize it. Here we evaluated the effect of a magnetic field (B) on the corrosion of copper in aqueous HCl solution under open circuit potential. The corrosion product, Cu2+, is a paramagnetic ion and its concentration in the solution was determined in real time in the corrosion cell by time-domain NMR relaxometry. The results show that the magnetic field (B = 0.23 T) of the time-domain NMR instrument reduces the corrosion rate by almost 50%, in comparison to when the corrosion reaction is performed in the absence of B. Atomic force microscopy and X-ray diffraction results of the analysis of the corroded surfaces reveal a detectable CuCl phase and an altered morphology when B is present. The protective effect of B was explained by magnetic forces that maintain the Cu2+ in the solution/metal interface for a longer time, hindering the arrival of the new corrosive agents, and leading to the formation of a CuCl phase, which may contribute to the rougher surface. The time-domain NMR method proved to be useful to study the effect of B in the corrosion of other metals or other corrosive liquid media when the reactions produce or consume paramagnetic ions.

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Garcia, Rodrigo Henrique dos Santos, Jefferson Gonçalves Filgueiras, Luiz Alberto Colnago et Eduardo Ribeiro de Azevedo. « Real-Time Monitoring Polymerization Reactions Using Dipolar Echoes in 1H Time Domain NMR at a Low Magnetic Field ». Molecules 27, n^o 2 (17 janvier 2022) : 566. http://dx.doi.org/10.3390/molecules27020566.

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1H time domain nuclear magnetic resonance (1H TD-NMR) at a low magnetic field becomes a powerful technique for the structure and dynamics characterization of soft organic materials. This relies mostly on the method sensitivity to the 1H-1H magnetic dipolar couplings, which depend on the molecular orientation with respect to the applied magnetic field. On the other hand, the good sensitivity of the 1H detection makes it possible to monitor real time processes that modify the dipolar coupling as a result of changes in the molecular mobility. In this regard, the so-called dipolar echoes technique can increase the sensitivity and accuracy of the real-time monitoring. In this article we evaluate the performance of commonly used 1H TD-NMR dipolar echo methods for probing polymerization reactions. As a proof of principle, we monitor the cure of a commercial epoxy resin, using techniques such as mixed-Magic Sandwich Echo (MSE), Rhim Kessemeier—Radiofrequency Optimized Solid Echo (RK-ROSE) and Dipolar Filtered Magic Sandwich Echo (DF-MSE). Applying a reaction kinetic model that supposes simultaneous autocatalytic and noncatalytic reaction pathways, we show the analysis to obtain the rate and activation energy for the epoxy curing reaction using the NMR data. The results obtained using the different NMR methods are in good agreement among them and also results reported in the literature for similar samples. This demonstrates that any of these dipolar echo pulse sequences can be efficiently used for monitoring and characterizing this type of reaction. Nonetheless, the DF-MSE method showed intrinsic advantages, such as easier data handling and processing, and seems to be the method of choice for monitoring this type of reaction. In general, the procedure is suitable for characterizing reactions involving the formation of solid products from liquid reagents, with some adaptations concerning the reaction model.

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Nikolskaya, Ekaterina, et Yrjö Hiltunen. « Time-Domain NMR in Characterization of Liquid Fuels : A Mini-Review ». Energy & ; Fuels 34, n^o 7 (12 juin 2020) : 7929–34. http://dx.doi.org/10.1021/acs.energyfuels.0c01464.

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Clayden, N. J., R. J. Lehnert et S. Turnock. « Factor analysis of time domain NMR data : crystallinity of poly(tetrafluoroethene) ». Analytica Chimica Acta 344, n^o 3 (juin 1997) : 261–69. http://dx.doi.org/10.1016/s0003-2670(97)00058-5.

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Clayden, N. J. « Factor analysis of simulated time domain NMR data for semicrystalline polymers ». Analytica Chimica Acta 356, n^o 1 (décembre 1997) : 27–33. http://dx.doi.org/10.1016/s0003-2670(97)00517-5.

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Rutledge, D. N. « Characterisation of water in agro-food products by time domain-NMR ». Food Control 12, n^o 7 (octobre 2001) : 437–45. http://dx.doi.org/10.1016/s0956-7135(01)00060-3.

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Nordon, Alison, Paul J. Gemperline, Colin A. McGill et David Littlejohn. « Quantitative Analysis of Low-Field NMR Signals in the Time Domain ». Analytical Chemistry 73, n^o 17 (septembre 2001) : 4286–94. http://dx.doi.org/10.1021/ac0102866.

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Gesmar, Henrik, et Jens J. Led. « Spectral estimation of complex time-domain NMR signals by linear prediction ». Journal of Magnetic Resonance (1969) 76, n^o 1 (janvier 1988) : 183–92. http://dx.doi.org/10.1016/0022-2364(88)90215-6.

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van Duynhoven, John, Isabelle Dubourg, Gert-Jan Goudappel et Eli Roijers. « Determination of MG and TG phase composition by time-domain NMR ». Journal of the American Oil Chemists' Society 79, n^o 4 (avril 2002) : 383–88. http://dx.doi.org/10.1007/s11746-002-0493-7.

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Labbé, Nicole, Bernard De Jéso, Jean-Claude Lartigue, Gérard Daudé, Michel Pétraud et Max Ratier. « Time-domain 1H NMR characterization of the liquid phase in greenwood ». Holzforschung 60, n^o 3 (1 mai 2006) : 265–70. http://dx.doi.org/10.1515/hf.2006.043.

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Abstract The time domain of 1H NMR spectroscopy allows straightforward editing of the T 2 relaxation profiles in maritime pine wood. A new method from the Carr-Purcell-Meiboom-Gill sequence is proposed to measure the amount and distribution of water in wood, as well as the location of major dissolved organic materials. A general calibration model giving reliable and precise identification of these parameters is described. The method presented for editing T 2 relaxation profiles (obtained by the Contin program) may be helpful in solving practical drying and gluing problems in the wood industry. It can be used for monitoring chemical modifications of wood fibers involved in the design of wood composite materials.

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Oleskevich, D. A., N. Ghahramany, W. P. Weglarz et H. Peemoeller. « Interfacial Spin–Spin Coupling in Wood by 2D Time-Domain NMR ». Journal of Magnetic Resonance, Series B 113, n^o 1 (octobre 1996) : 1–8. http://dx.doi.org/10.1006/jmrb.1996.0148.

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Geil, B., F. Fujara et H. Sillescu. « 2H NMR Time Domain Analysis of Ultraslow Reorientations in Supercooled Liquids ». Journal of Magnetic Resonance 130, n^o 1 (janvier 1998) : 18–26. http://dx.doi.org/10.1006/jmre.1997.1284.

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Linke, Christina, Gisela Guthausen, Eckhard Flöter et Stephan Drusch. « Solid Fat Content Determination of Dispersed Lipids by Time-Domain NMR ». European Journal of Lipid Science and Technology 120, n^o 4 (19 février 2018) : 1700132. http://dx.doi.org/10.1002/ejlt.201700132.

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Webber, J. Beau W. « Some Applications of a Field Programmable Gate Array Based Time-Domain Spectrometer for NMR Relaxation and NMR Cryoporometry ». Applied Sciences 10, n^o 8 (15 avril 2020) : 2714. http://dx.doi.org/10.3390/app10082714.

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NMR Relaxation (NMRR) is an extremely useful quantitative technique for material science, particularly for studying polymers and porous materials. NMR Cryoporometry (NMRC) is a powerful technique for the measurement of pore-size distributions and total porosities. This paper discusses the use, capabilities and application of a newly available compact NMR time-domain relaxation spectrometer, the Lab-Tools Mk3 NMR Relaxometer & Cryoporometer [Lab-Tools (nano-science), Ramsgate, Kent, UK (2019)]. Being Field Programmable Gate Array based means that it is unusually compact, which makes it particularly suitable for the lab bench-top, in the field and also mobile use. Its use with a variable-temperature NMR probe such as the Lab-Tools Peltier thermo-electrically cooled variable-temperature (V-T) probe is also discussed. This enables the NMRC measurement of pore-size distributions in porous materials, from sub-nano- to over 1 micron sized pores. These techniques are suitable for a wide range of porous materials and also polymers. This instrument comes with a Graphical User Interface (GUI) for control, which also enables both online and offline analysis of the measured data. This makes it is easy to use for material science studies both in the field and in university, research institute, company and even school laboratories. The Peltier cooling gives the precision temperature control and smoothness needed by NMR Cryoporometry, particularly near the probe liquid bulk melting point. Results from example NMR Relaxation and NMR Cryoporometric measurements are given.

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Slijkerman, W. F. J., W. J. Looyestijn, P. Hofstra et J. P. Hofman. « Processing of Multi-Acquisition NMR Data ». SPE Reservoir Evaluation & ; Engineering 3, n^o 06 (1 décembre 2000) : 492–97. http://dx.doi.org/10.2118/68408-pa.

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Summary Crucial issues in formation evaluation are the determination of porosity, permeability, hydrocarbon volumes, and net-to-gross ratio. Nuclear magnetic resonance (NMR) logging provides measurements that are directly related to these parameters. The NMR response of fluids contained in pores is governed by their T2- and T1-relaxation times, diffusion coefficient, and whether or not they wet the rock. In the case where fluids possess a sufficiently large contrast in these properties and NMR data have been acquired with suitably chosen acquisition parameters (i.e., wait times and/or inter-echo times) a separation of water, oil, and gas NMR responses can be made. From these separate NMR responses the hydrocarbon volumes, porosity, and permeability estimates are subsequently calculated. Key in these applications is the ability to include all the acquired log NMR data into the processing towards the desired end result. Methods exist to derive hydrocarbon volumes from T2 distributions or from echo decay data. However, these are all methods in which the difference between just two acquisitions that only differ in either wait time or inter-echo time are considered. Over the past years we have developed, tested, and employed an alternative processing technique named multi-acquisition NMR (MacNMR). MacNMR takes any number of log acquisitions (wait time and/or inter-echo time variations) and simultaneously inverts them using a rigorous forward model to derive the desired water and hydrocarbon T2 distributions. In this paper, we discuss the concepts of MacNMR and demonstrate its versatility in NMR log processing. An example will illustrate its benefits. Introduction This paper discusses the method used by Shell to process multi-acquisition nuclear magnetic resonance (NMR) data. The objective of the processing is to extract fluid volumes and properties from multi-acquisition NMR data. The potential of multi-acquisition NMR logging for water, oil, and gas discrimination and volume quantification was recognized already in 1993. At that time no commercial processing of such data was available. It was decided to develop an in-house multi-acquisition processing capability. From 1993 to 1996 the development effort was focused on the evaluation of potential processing concepts and the development of the necessary mathematical algorithms. In 1996 the actual software implementation was developed, and in October 1996 first results were available and published internally. In March 1997 a company-wide beta test of the software was organized. In August 1997 the software was released company wide and has been in use since then. Multi-Acquisition Data Processing Methods As an introduction, we briefly review methods for quantitative processing of multi-acquisition NMR data that are described in the open literature. We make the distinction between methods that operate in the relaxation time domain vs. methods that operate in the acquisition time domain. Analysis in the Relaxation Time (or T2) Domain. Here, methods are discussed that operate in the T2 domain. Differential Spectrum Method. The differential spectrum method, first published by Akkurt and Vinegar1 works on dual-wait-time data. The concept is to independently T2 invert the long- and short-wait-time echo-decay vectors into a T2 spectrum. The two resulting T2 spectra are subtracted and, provided the wait times have been selected suitably,2 the difference between the two T2 spectra only arises from fluids with long T1 components (usually hydrocarbons). Volumes are quantified by integrating the difference T2 spectrum and correcting for the polarization difference between long and short wait time. Enhanced Diffusion Method. The enhanced diffusion method, recently published by Akkurt et al., 3 exploits the diffusion contrast between the diffusive brine and the less diffusive (medium-to-heavy) oil (i.e., water diffusion is faster than oil diffusion). The idea is that the inter-echo time is chosen sufficiently long such that the water and oil signals are fully separated in the T2 domain (i.e., water is at lower T2 than oil). Determining oil volumes is then just a matter of integrating over the appropriate T2 range in the T2 spectrum. Analysis in the Acquisition Time Domain. Here, methods are discussed that operate in the acquisition time domain. Time-Domain Analysis. The time-domain analysis method (TDA) operates on dual-wait-time data. This method was first published by Prammer et al.4 The concept is to subtract the measured long- and short-wait-time decay vectors into an echo difference. In case the wait times have been chosen suitably2 the difference of the two decay vectors should be arising from a long T1 component (usually a hydrocarbon). This difference echo vector is subsequently T2 inverted (using "matched filters," which basically means that a uni- or bi-exponential is fitted to the data). In that way, only the T2 component arising from the hydrocarbon is found. The hydrocarbon volume is deduced by correcting the resulting signal strength from the difference in polarization between long and short wait time. Echo Ratio Method. This method, published by Flaum et al.,5 works on dual-inter-echo-time data. The long- and short-inter-echo-time echo decays are divided and an apparent diffusion coefficient is calculated. The apparent diffusion coefficient can be used as a qualitative indicator for the presence of gas. MacNMR Method MacNMR uses a method that is radically different from the other processing schemes and is a comprehensive implementation of earlier concepts.1,6 MacNMR employs a forward model to model the measured echo-decay vectors. The starting points in the forward model are the T2 spectra for each of the fluids present (water, oil, and/or gas) that would be measured at infinite wait time and zero gradient. From these T2 spectra, echo-decay vectors are constructed by accounting for the effects of hydrogen index, polarization, and diffusion. The best-fit T2 spectra are found by inverting the forward model to the measured echo-decay vectors. All measured echo-decay vectors included in the inversion are treated on an equal statistical footing. They are weighted with their respective rms-noise values. Hence, decays with the lowest noise contribute most. In principle, any number of echo-decay vectors can be included in the inversion. The current software implementation of MacNMR accepts up to a maximum of six echo-decay vectors, totaling a maximum of 7,000 echoes. The inversion typically takes less than 1 second per depth increment. In a sense, MacNMR employs a very classical concept in that it defines unknown variables (T2 spectra for the fluids present) that are determined from the available data (i.e., all the acquired decay vectors) by error minimization. Between the unknown variables and the data is a forward model. The forward model contains the effects of inter-echo-time variation and wait-time variation. Analysis in the Relaxation Time (or T2) Domain. Here, methods are discussed that operate in the T2 domain. Differential Spectrum Method. The differential spectrum method, first published by Akkurt and Vinegar1 works on dual-wait-time data. The concept is to independently T2 invert the long- and short-wait-time echo-decay vectors into a T2 spectrum. The two resulting T2 spectra are subtracted and, provided the wait times have been selected suitably,2 the difference between the two T2 spectra only arises from fluids with long T1 components (usually hydrocarbons). Volumes are quantified by integrating the difference T2 spectrum and correcting for the polarization difference between long and short wait time. Enhanced Diffusion Method. The enhanced diffusion method, recently published by Akkurt et al.,3 exploits the diffusion contrast between the diffusive brine and the less diffusive (medium-to-heavy) oil (i.e., water diffusion is faster than oil diffusion). The idea is that the inter-echo time is chosen sufficiently long such that the water and oil signals are fully separated in the T2 domain (i.e., water is at lower T2 than oil). Determining oil volumes is then just a matter of integrating over the appropriate T2 range in the T2 spectrum. Analysis in the Acquisition Time Domain. Here, methods are discussed that operate in the acquisition time domain. Time-Domain Analysis. The time-domain analysis method (TDA) operates on dual-wait-time data. This method was first published by Prammer et al.4 The concept is to subtract the measured long- and short-wait-time decay vectors into an echo difference. In case the wait times have been chosen suitably2 the difference of the two decay vectors should be arising from a long T1 component (usually a hydrocarbon). This difference echo vector is subsequently T2 inverted (using "matched filters," which basically means that a uni- or bi-exponential is fitted to the data). In that way, only the T2 component arising from the hydrocarbon is found. The hydrocarbon volume is deduced by correcting the resulting signal strength from the difference in polarization between long and short wait time. Echo Ratio Method. This method, published by Flaum et al.,5 works on dual-inter-echo-time data. The long- and short-inter-echo-time echo decays are divided and an apparent diffusion coefficient is calculated. The apparent diffusion coefficient can be used as a qualitative indicator for the presence of gas.

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Declerck, Arnout, Veronique Nelis, Sabine Danthine, Koen Dewettinck et Paul Van der Meeren. « Characterisation of Fat Crystal Polymorphism in Cocoa Butter by Time-Domain NMR and DSC Deconvolution ». Foods 10, n^o 3 (2 mars 2021) : 520. http://dx.doi.org/10.3390/foods10030520.

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The polymorphic state of edible fats is an important quality parameter in fat research as well as in industrial applications. Nowadays, X-ray diffraction (XRD) is the most commonly used method to determine the polymorphic state. However, quantification of the different polymorphic forms present in a sample is not straightforward. Differential Scanning Calorimetry (DSC) is another method which provides information about fat crystallization processes: the different peaks in the DSC spectrum can be coupled to the melting/crystallisation of certain polymorphs. During the last decade, nuclear magnetic resonance (NMR) has been proposed as a method to determine, qualitatively and/or quantitatively, the polymorphic forms present in fat samples. In this work, DSC- and NMR-deconvolution methods were evaluated on their ability to determine the polymorphic state of cocoa butter, with XRD as a reference method. Cocoa butter was subjected to two different temperature profiles, which enforced cocoa butter crystallization in different polymorphic forms. It was found that XRD remains the best method to qualitatively determine the polymorphic state of the fat. Whereas the quantitative NMR and DSC deconvolution results were not fully in line with the XRD results in all cases, NMR deconvolution showed great promise both in a qualitative and quantitative way.

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Tas, Ozan, Ulku Ertugrul, Leonid Grunin et Mecit Halil Oztop. « Investigation of the Hydration Behavior of Different Sugars by Time Domain-NMR ». Foods 11, n^o 8 (15 avril 2022) : 1148. http://dx.doi.org/10.3390/foods11081148.

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The hydration behavior of sugars varies from each other and examining the underlying mechanism is challenging. In this study, the hydration behavior of glucose, fructose, allulose (aka rare sugar), and sucrose have been explored using different Time Domain Nuclear Magnetic Resonance (TD-NMR) approaches (relaxation times, self-diffusion, and Magic Sandwich Echo (MSE)). For that purpose, the effects of different sugar concentrations (2.5%, 5%, 10%, 15%, 20%, 30%, and 40%) (w/v) and hydration at different times for 1 day were investigated by T2 relaxation times and self-diffusion coefficients. Crystallinity values of the solid and hydrated sugars were also determined with MSE. Change in T2 relaxation times with concentration showed that the fastest binding with water (parallel with the shortest T2 values) was observed for sucrose for all concentrations followed by glucose, fructose, and allulose. Furthermore, dependency of T2 relaxation times with hydration time showed that sucrose was the fastest in binding with water followed by glucose, fructose, and allulose. The study showed that allulose, one of the most famous rare sugars that is known to be a natural low-calorie sugar alternative, had the lowest interaction with water than the other sugars. TD-NMR was suggested as a practical, quick, and accurate technique to determine the hydration behavior of sugars.

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Fritzsching, Keith J., Yizhuo Yang, Emily M. Pogue, Joseph B. Rayman, Eric R. Kandel et Ann E. McDermott. « Micellar TIA1 with folded RNA binding domains as a model for reversible stress granule formation ». Proceedings of the National Academy of Sciences 117, n^o 50 (30 novembre 2020) : 31832–37. http://dx.doi.org/10.1073/pnas.2007423117.

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TIA1, a protein critical for eukaryotic stress response and stress granule formation, is structurally characterized in full-length form. TIA1 contains three RNA recognition motifs (RRMs) and a C-terminal low-complexity domain, sometimes referred to as a “prion-related domain” or associated with amyloid formation. Under mild conditions, full-length (fl) mouse TIA1 spontaneously oligomerizes to form a metastable colloid-like suspension. RRM2 and RRM3, known to be critical for function, are folded similarly in excised domains and this oligomeric form of apo fl TIA1, based on NMR chemical shifts. By contrast, the termini were not detected by NMR and are unlikely to be amyloid-like. We were able to assign the NMR shifts with the aid of previously assigned solution-state shifts for the RRM2,3 isolated domains and homology modeling. We present a micellar model of fl TIA1 wherein RRM2 and RRM3 are colocalized, ordered, hydrated, and available for nucleotide binding. At the same time, the termini are disordered and phase separated, reminiscent of stress granule substructure or nanoscale liquid droplets.

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Djermoune, E. H., M. Tomczak et D. Brie. « NMR Data Analysis : A Time-Domain Parametric Approach Using Adaptive Subband Decomposition ». Oil & ; Gas Science and Technology – Revue d’IFP Energies nouvelles 69, n^o 2 (28 mars 2013) : 229–44. http://dx.doi.org/10.2516/ogst/2012092.

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Munaro, Ana P., Giovanni P. da Cunha, Jefferson G. Filgueiras, José M. Pinto, Marilda Munaro, Eduardo R. de Azevedo et Leni C. Akcelrud. « Ageing and structural changes in PDMS rubber investigated by time domain NMR ». Polymer Degradation and Stability 166 (août 2019) : 300–306. http://dx.doi.org/10.1016/j.polymdegradstab.2019.06.008.

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Felby, Claus, Lisbeth G. Thygesen, Jan B. Kristensen, Henning Jørgensen et Thomas Elder. « Cellulose–water interactions during enzymatic hydrolysis as studied by time domain NMR ». Cellulose 15, n^o 5 (6 mai 2008) : 703–10. http://dx.doi.org/10.1007/s10570-008-9222-8.

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Nikolskaya, Ekaterina, et Yrjö Hiltunen. « Molecular Properties of Fatty Acid Mixtures Estimated by Online Time-Domain NMR ». Applied Magnetic Resonance 50, n^o 1-3 (31 juillet 2018) : 159–70. http://dx.doi.org/10.1007/s00723-018-1046-6.

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